南乌拉尔地区中—新元古代地层序列及碳酸盐岩和碎屑岩发现臼齿构造的地质意义

Meso-and Neoproterozoic stratigraphic sequences in the Southern Ural area and discovery of molar-tooth structures in carbonate and clastic rocks of the sequences and their geological significance

中—新元古代地层在南乌拉尔海槽中极为发育,地层厚度巨大,几个阶段的构造演化和沉积特征清晰可见。新太古代和下里菲是俄罗斯重要的大型层状铁矿和菱镁矿的宿主地层,中里菲群(元古宙地层)地层厚度极大,伴随了几次沉积旋回,发育了从深海相到大陆缓坡的碳酸盐岩沉积;随着新元古代末次冰期之后,文德系发育了可全球对比的白海动物群(伊迪卡拉动物群)。笔者首次确认了南乌拉尔地区中—新元古代地层3套臼齿构造,其中巴卡尔组(Bakal)碳酸盐岩臼齿构造与碎屑岩地震液化脉互层共生,特别是大量臼齿构造也发育在大型叠层石中。从臼齿构造与碎屑岩液化脉互层的共生特征,说明发育在碳酸盐岩中臼齿构造与地震机理的液化作用有关。该3套臼齿构造与中国华北地台中—新元古代地层中发现的臼齿构造(液化脉)时代大体接近。

Meso-and Neoproterozoic strata are very well developed in the southern Ural Trough. They have a huge thickness and show distinct features of tectonic evolution and deposition of several stages. The Neoarchean and Lower P, iphean are important host strata of large stratabound iron and magnesite deposits. The Middle Riphean （Mesoproterozoic） has very thick deposits with several depositional cycles, when carbonate rocks of abyssal to ramp facies were developed. After the Neoproterozoic last glaciation, the White Sea fauna （Ediacaran fauna）, which may be used for global correlation, appeared in the Vendian System. The authors for the first time recognize three sets of molar-tooth structures in the Meso- and Neoproterozoic strata of the Southern Ural area. Of these, the molar-tooth structure in carbonate rocks of the Bakal Formation alternates and is associated with seismic liquefied veins, and even the molar-tooth structures are also developed in large-scale stromatolites in the lower Riphean Staka and Bakal formations. This feature indicates that the molar-tooth structure in carbonate rocks is related to seismic liquefaction. The age of the three sets of molar-tooth structures is largely close to that of the molar-tooth structure （liquefied vein） found in the Meso- and Neoproterozoic strata in the North China block.